I was involved in a street fight under film.

I'll begin this by telling that I'm not a guy who fights alot. Opposite is true. I resent violence and I try to avoid it at all costs. This situation got me really offguard. Me and my friend went to the gym from our boarding school. When we were on our way back, a guy approached us and started screaming at us:"WHY DID YOU MESS WITH HIM"? and pointed at his friend from behind who was filming the whole thing. Both me and my friend had no clue what he was talking about. I told him that we didn't talk to him and we do not know him. He kept asking it like 4 more times untill he started pushing me. My friend pushed him back and I didn't expect it but a second after it I was punched in the face. After realizing I've been punched like 5 seconds later (I got a small concussion but managed to see well after) my friend jumped on him and held him and I threw a punch straight at his nose and got him knocked out. After that both me and my friend ran away as we were afraid they would have a knife or/and there were more of them. Since that I'm always alerted and uneasy near every person that looks even a little bit suspicious to me and it feels really bad.